Many types of liquid level sensing devices have been disclosed in the prior art. Such devices, which are usually based on magnetic, electrical conductivity, acoustic or optical parameters, enable user manipulation of the positioning of the sensing elements for either facilitating the operation of the liquid level sensor itself or the issue of a sensible output at a desired liquid level in the monitored vessel, in accordance with one or more predetermined sensing elements. Thus, for example, U.S. Pat. Nos. 3,696,362 and 3,944,845 describe conducting liquid level control devices, which indicate when the level of a conducting liquid reaches a predetermined minimum level, while U.S. Pat. No. 4,354,180 describes an optical liquid level sensing probe. U.S. Pat. Nos. 3,849,771 and 4,771,272 describe portable self-contained liquid level alarm devices having a housing in which a floating magnet actuates a reed switch. U.S. Pat. No. 3,702,910 describes a level sensing control device with a reed switch which can be rotatably adjusted to any position in respect of a magnetic member connected to a float member. Additional implementations of such magnetic devices have been described inter alia in U.S. Pat. Nos. 3,702,910; 3,823,328; 3,997,744; 3,978,299; 4,035,789; 4,066,858; 4,395,605; 4,458,118; 4,459,584; 4,499,348; 4,609,796; 4,748,299; 4,748,300; 5,103,673; 5,224,379; 5,426,271; 5,562,003; and 5,565,687.
U.S. Pat. No. 5,565,607 describes an apparatus that comprises a linear series of switches, each of which is closed when in the proximity of an actuating magnet movable along the series of switches. Movement of the magnet produces a progressive change in voltage on the output line, a resistance chain linked to the switches, as a cumulative signal indicating the position of the magnet. A cumulative signal represented in the magnet position relative to the series of switches can thus be generated.
U.S. Pat. No. 4,771,272 discloses an indicator of a liquid level which comprises a pendant liquid level sensor suspended at a desired height within a vessel by means of flexible cable, said sensor including a hollow, elongated cylindrical housing closed at both the upper and the lower end by cylindrical cups providing the perforations to permit water to enter or exit. A cylindrical float is contained coaxially within the housing, and has a permanent magnet recessed into its upper surface. The switch is closed when the magnet rises sufficiently to contact or to almost contact it.
Most of the liquid level monitoring and alarm systems described in the prior art, including those based on a floating magnet, are not versatile and usually have drawbacks and/or are not convenient for user manipulation. It is especially seen in cases in which the monitored vessel's interior is wholly inaccessible, such as the case of a sealed vessel holding hazardous material or when the content and/or prevailing conditions do not allow a simple and convenient user access and manipulation. Similar difficulties exist in the case of heated vessels, particularly in the case of a cooking pot or the like.
It is often found in everyday cooking operations that a heated liquid, e.g., soup, is left simmering on a heat source without supervision. It may happen that the cooking pot on the heat source has been forgotten, whereby the victuals being cooked or the cooking pot itself may be ruined and, more seriously, a hazardous situation may develop. There are known devices for automatically switching off an electrical water heater when the water level drops below the level of the heating element of the heater. Also, U.S. Pat. No. 4,673,925 describes an alarm device, for removably mounting onto the upper edge of a cooking pot, which provides an alarm when the liquid contents of the cooking pot begin to boil, whilst U.S. Pat. No. 5,229,751 describes a coffee pot including an integrally provided alarm device for providing a time-based alarm indication in respect of the freshness of its liquid contents. Also, U.S. Pat. No. 5,341,728 describes an alarm device, which controls the cooker and indicates the end of cooking timing.
Also, an appropriate apparatus for monitoring and controlling the liquid level in a cooking vessel is specially needed for blind or visually impaired individuals. It would be very helpful, to those individuals, to have a device by which they will be able to monitor easily the liquid level in their cooking vessel. Thus, for example, it would be very helpful to visually impaired individuals who would like to boil water for preparing a cup of coffee, if they could be provided with an appropriate and simple device by which they could, whenever they like, monitor the liquid level in the kettle.
In reality, only certain household containers, for example, electric kettles, are provided with liquid level sensors and automatic alarms or switch-off devices, while most cooking pots and pans do not include such devices. This is primarily because the liquid level sensors and/or auto-switch devices of the art consume valuable space and interfere in cooking/cleaning operations. Moreover, even liquid level sensing devices currently used for cooking apparatus do not contain a simple and convenient means allowing the user, whenever he or she desires, to easily change the level at which the sensor will activate the alarm.
It is a purpose of this invention to provide a liquid level monitoring and control apparatus that generates an alarm, a safety signal or other output signal when the liquid reaches a predetermined level or when an actuator and an appropriate actuatable-switch are positioned within their actuation range.
It is further purpose of the present invention, to provide a liquid level monitoring and control apparatus that can be used by blind or visually impaired individuals.
It is a still further object to provide such an apparatus that enables convenient user access to level setting components.
It is a still further object of the present invention to provide a liquid level sensor that is exceptionally versatile, in that the same general structure of sensor is suitable, with minor modifications, for obtaining a liquid-level apparatus whose operation can be based on various types of physical properties such as; magnetic, acoustic, electrical conductivity and electromagnetic radiation (hereinafter also "optical-radiation").
It is a still further object to provide such an apparatus that may be designed so as to be usable with a variety of vessels of different sizes and shapes, with both open and sealed vessels, and with vessels with an interior inaccessible to user manipulation.
It is a still further object to provide a novel and versatile liquid level sensor that can be readily adapted for a wide range of applications.
It is a still further object of the present invention to provide a liquid level apparatus that is applicable also for liquid containing solid materials.
It is a still further object to provide a liquid level monitoring and control apparatus that is particularly suited for use with cooking vessels.
It is a still further object to provide an alarm kit that is portable, transferable, and used interchangeably with a wide variety of vessels.
It is a still further object to provide such an apparatus that is compact and inexpensive.
It is a further object of the present invention to provide elements that are multifunction.
Other purposes and advantages of the invention will appear as the description proceeds.